In a field of the chemical industry, various solid-liquid contact apparatuses are used for performing operation such as washing, purification, extraction, impregnation, chemical reaction, and dissolution of the solid by causing the solid and the liquid to be contacted. As the solid-liquid contact apparatus, a column-type solid-liquid countercurrent contact apparatus (also, referred to as longitudinal solid-liquid countercurrent contact apparatus) is known in which the solid particles and the liquid are continuously subjected to the countercurrent contact as an upward flow and a downward flow, respectively.
The column-type solid-liquid countercurrent contact apparatus has an advantage of having high throughput capability compared to other solid-liquid contact apparatuses because of its high processing power and high contact efficiency between the solid particles and the liquid.
For example, Japanese Patent Publication (JP-B) No. 54-12265 (Patent Literature 1) discloses that an ingredient and a solvent are subjected to the countercurrent contact using a multi-step extraction apparatus that includes an extraction apparatus body, a step partitioning between the steps, a partitioning stirring blade, and a partitioning stirring shaft. WO 2005/33058 A1 (Patent Literature 2, and corresponding to US 2007/0015935 A1 and EP 1669343 A1) discloses a method of manufacturing terephtalic acid in which the countercurrent contact is performed using a column that includes a plurality of stirring blades in the vertical direction.
Also, WO 2005/32736 A1 (Patent Literature 3, and corresponding to US 2006/0254622 A1 and EP 1669140 A1) discloses a method and an apparatus of continuously washing the solid particles in which the solid particles are supplied from an upper part of a longitudinal washing tank to form a high concentration zone of the solid particles in the washing tank, and the high concentration zone is subjected to the countercurrent contact with an upward flow of the washing liquid while being stirred with a plurality of stirring blades.
Further, Japanese Patent Application Laid-Open (JP-A) No. 2008-513186 (Patent Literature 4, and corresponding to WO 2006/030588 A1) proposes a longitudinal solid-liquid countercurrent contact apparatus in which a plurality of stirring chambers mutually divided by a partitioning plate that has a communication opening, and connected in the vertical direction is provided, a radial ejection type stirring blade and one or more baffles fixed to an inner side of a side wall are provided in each stirring chamber, and a solid inlet and a liquid inlet are provided at an upper part and a lower part.
In these conventional column-type solid-liquid countercurrent contact apparatuses, by providing a plurality of stirring blades and divided chambers, the solid-liquid contact is sufficiently performed while the solid particles move in the longitudinal direction. The column-type solid-liquid countercurrent contact apparatus is expected to have high processing power, and moreover, to perform highly-efficient and uniform contact with a small amount of the solid-liquid contact. To enhance the contact efficiency in the solid-liquid countercurrent contact apparatus, it is necessary to continuously and rapidly renew a contact interface between the solid particles and the liquid.
Therefore, the conventional column-type solid-liquid countercurrent contact apparatus is provided with a plurality of divided chambers connected in the longitudinal direction via a communication opening, and a stirring blade is provided in each divided chamber. The contact interface between the solid particles and the liquid is continuously and rapidly renewed by stirring with the stirring blade. Accordingly, the solid particles after the contact process are moved and settled in the next divided chamber by an action of gravity, and the contact process with a new liquid flowing upward is performed. The above processes are repeated.
However, the contact efficiency between the solid particles and the liquid has not yet been sufficient. That is, in the divided chamber provided with a stirring blade (hereinafter, referred to as “stirring chamber”), the following phenomena might happen: a renewal speed of the contact interface between the solid particles and the liquid becomes non-uniform, backmixing occurs in which the solid particles after contact process in the stirring chamber is again in contact with the liquid with which the contact process has been already performed instead of a new liquid, non-uniformity occurs in moving time of the solid particles settling from one stirring chamber to a lower connected stirring chamber, and in some cases, the solid particles after being subjected to the contact process in the stirring chamber pass through the communication opening by accompanying the upward flow of the liquid, and flow backward to an upper connected stirring chamber.
If these phenomena occur, not only is the processing efficiency of the column-type solid-liquid countercurrent contact apparatus lowered, but also the time of being subjected to the solid-liquid countercurrent contact per solid particle differs, whereby uniformity of quality of the solid particles which are subjected to the solid-liquid countercurrent contact process and recovered as products is lost. Therefore, improvement of the apparatus has been sought.
As the stirring blade used in the solid-liquid countercurrent contact apparatus, a paddle blade such as a flat paddle blade, an inclined paddle blade, a V-type paddle blade, a pfaudler blade, or a brumargin blade, a turbine blade such as a turbine blade or a fan turbine blade, and a propeller blade such as a marine propeller blade are known. Among these blades, it is known that the paddle blade and the turbine blade are more likely to generate mainly the flow in a blade radial direction by a centrifugal action of blade rotations, whilst the propeller blade is more likely to generate the flow in an axial direction by thrust in the direction of the rotating shaft. It is also known that, in both cases, the direction of the flow to be generated is adjustable to some extent by changing a shape, an attaching angle of the blade, or the like.
The stirring blade provided in the stirring chamber of the column-type solid-liquid countercurrent contact apparatus is required to cause the solid particles to stay in the stirring chamber for a predetermined time, and to be subjected to the solid-liquid contact. When the propeller blade is used as the stirring blade, which generates the flow mainly in the axial direction, the solid particles supplied from above are more likely to be discharged from the stirring chamber in a relatively short time due to the downward flow of the axial direction. In contrast, when the paddle blade or the turbine blade is used, the flow rotating in the stirring chamber can cause the solid particles to stay in the stirring chamber for a relatively long time.
The solid particles subjected to the solid-liquid contact in the stirring chamber are gradually settled by an action of gravity, and are discharged to a lower connected stirring chamber through the communication opening. A staying time of the solid particles in the stirring chamber is adjustable by changing a shape of a blade, an attaching angle, and a rotation speed of the paddle blade or of the turbine blade.
Therefore, the paddle blade or the turbine blade is preferably used as the stirring blade provided in the stirring chamber of the column-type solid-liquid countercurrent contact apparatus. Among these blades, the paddle blade is widely employed because of its simple structure, low manufacturing cost, and low maintenance cost, wherein the paddle blade is formed of an approximately planar vane plate that is radially provided to a rotating shaft in a protruding manner.
However, when the paddle blade is employed as the stirring blade provided in the stirring chamber of the column-type solid-liquid countercurrent contact apparatus, the above-described inconvenient phenomena occur relatively remarkably, the inconvenient phenomena being such that not only is the processing efficiency of the column-type solid-liquid countercurrent contact apparatus lowered, but also the time of being subjected to the solid-liquid countercurrent contact per solid particle differs, whereby uniformity of quality of the solid particles which are subjected to the solid-liquid countercurrent contact process and recovered as products is lost. Therefore, improvement has been strongly sought. Improvement can be achieved to some extent by decreasing a flow rate of the solid particles and the liquid, or by decreasing the cross-sectional area of the communication opening of each stirring chamber in the horizontal direction. However, as a result, the processing power is significantly decreased.
The inventors diligently proceeded with a study on generation mechanism of the above-described inconvenient phenomena that occur when the paddle blade is employed as the stirring blade provided in the stirring chamber of the column-type solid-liquid countercurrent contact apparatus. As a result, it has been found out that occurrence of a short path is the major reason, where the solid particles in the vicinity of the rotating shaft, to which the paddle blade is fixed, are discharged from the stirring chamber without being subjected to the solid-liquid countercurrent contact in the stirring chamber for a sufficient time.
The paddle blade is a stirring blade wherein typically two to eight approximately planar vane plates are radially provided to the rotating shaft at even intervals in a protruding manner, and causes the liquid to flow mainly in a radial direction by rotating the rotating shaft in the liquid. Especially, the flat paddle blade causes the flow mostly in the radial direction wherein a planar vane plate is provided parallel to the axial direction of the rotating shaft in a protruding manner. However, in a case of the inclined paddle blade, the proportions of the flows generated in the radial and axial directions are changed depending on an inclined angle. Also, in a case of the pfaudler blade, the proportion of the flow in the axial direction is large. That is, in the case of the paddle blade, the ratio between the flows in the radial and axial directions caused in the stirring chamber is adjustable by changing the shape, the size, the attaching angle of the vane plate, and the like.
The rotation of the paddle blade causes the flow of the liquid in the stirring chamber mainly in the radial direction, whereby the solid particles are not discharged from the stirring chamber in a short time, and the solid particles and the liquid can contact each other while staying in the stirring chamber and renewing the contact interface.
In a case where the density of the solid particles is larger than that of the liquid, the solid particles are gradually settled in the liquid by an action of gravity. In the stirring chamber, typically, about two to eight baffles, which extend in the vertical direction along an inner wall surface, are provided in the radial direction at even intervals in a protruding manner, whereby the flow of the liquid being stirred up and down can be caused as well as the flow in the radial or circumferential direction. Therefore, the settlement of the solid particles is alleviated. Also, by disposing the baffle, a hindrance to the renewal of the contact interface due to corotation of the solid particles and the liquid can be prevented.
In this way, for a given length of time, the solid particles are gradually settled in the stirring chamber while being subjected to the solid-liquid contact process, and pass through the communication opening to be discharged into a lower connected stirring chamber. Thus, the solid particles gradually flow downward whilst the liquid flows upward so that the solid-liquid countercurrent contact is performed in the apparatus.
The paddle blade is formed of an approximately planar vane plate being radially provided to the rotating shaft at even intervals in a protruding manner, and a turning angle velocity of the vane plate is increased in proportion to the distance from the rotating shaft. Meanwhile, the turning angle velocity of the approximately planar vane plate is small in the vicinity of the rotating shaft. Therefore, the flow of the liquid in the radial and circumferential directions becomes small, and the movement of the solid particles in the radial and circumferential directions becomes small. Further, in the vicinity of the rotating shaft, the influence of the flow being stirred up and down is small, where the flow is caused by the baffle provided on the inner wall surface of the column body part. The solid particles in the vicinity of the rotating shaft are gradually settled in the stirring chamber by an action of gravity under the condition of the solid particles being less likely to be influenced by the flow of the liquid being stirred up and down or by the flow of the liquid in the radial and circumferential directions. As a result, the solid particles in the vicinity of the rotating shaft are, without being subjected to the solid-liquid countercurrent contact for a sufficient time, more likely to pass through the communication opening along the axial direction of the rotating shaft in the stirring chamber and to be discharged into the lower connected stirring chamber in a relatively short time. Therefore, the solid particles discharged into a lower connected stirring chamber have a high probability of existing in the vicinity of the rotating shaft. Therefore, again, in the stirring chamber, the solid particles are, without being subjected to the solid-liquid countercurrent contact for a sufficient time, more likely to pass through the communication opening along the axial direction of the rotating shaft and to be discharged into a further lower connected stirring chamber in a relatively short time.
The inventors of the present invention have found out, in the column-type solid-liquid countercurrent contact apparatus, that the short path (S in FIG. 3) occurs wherein the solid particles are discharged from the apparatus without being substantially subjected to the solid-liquid countercurrent contact.
Further, the solid particles without being subjected to the solid-liquid countercurrent contact for a sufficient time increase due to the occurrence of the short path. Therefore, the inconvenience is caused wherein the processing efficiency of the column-type solid-liquid countercurrent contact apparatus is decreased, and the uniformity of quality of the solid particles recovered as a product is lost.
Meanwhile, to enhance the solid-liquid countercurrent contact efficiency, it is effective to increase the number of stirring rotations to facilitate the solid-liquid contact. However, as a result, the stirring power is increased, and up and down movement of the solid particles is facilitated. Accordingly, the solid particles flow back to an upper connected stirring chamber, and the uniformity of the solid-liquid countercurrent contact is impaired. Therefore, if the number of stirring rotations is increased too much, the contact efficiency is decreased accordingly. Furthermore, the number of stirring rotations at a low speed causes stagnation/settlement of the solid particles in the vicinity of a wall of the stirring chamber, whereby the effective volume of the stirring chamber as a space for the solid-liquid contact is decreased, and contact time of the solid and the liquid is decreased.